1. Field of the Invention
The present invention relates to a joined wafer composed of a semiconductor wafer having device formed areas in its surface and a transparent wafer which are stuck together, a fabrication method thereof, and a fabrication method of semiconductor devices comprising semiconductor chips into which the joined wafer is divided.
2. Description of the Related Art
In these years, as information processing apparatuses represented by, e.g., mobile phones become more advanced in functionality, smaller in size, and higher in component mounting density, semiconductor packages mounted in these information processing apparatuses are becoming considerably smaller. For example, as to mobile phones with a camera and digital cameras, it is desired that semiconductor packages having a solid-state image sensing device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) that are mounted in them be miniaturized. As a technology to achieve the miniaturization, a chip size packaging technology is attracting attention that realizes a package size substantially the same as the chip size.
A chip size package having an image sensing function is usually sealed with a glass substrate for reinforcement and protection. For example, Japanese Patent Application Laid-Open Publication No. 2007-282137 discloses a module for an optical device including a configuration where a solid-state image sensing device and a transparent lid are joined via an adhesive layer (see FIG. 1 of the publication). Further, Japanese Patent Application Laid-Open Publication No. 2004-207461 discloses a solid-state image sensing unit including a configuration where a solid-state image sensing device and an optical glass are joined via a junction layer (see FIG. 5 of the publication).
Conventionally, structures where a semiconductor chip having a solid-state image sensing device formed therein and a glass substrate are stuck together have been fabricated by the following process. First, a transparent wafer having flat opposite surfaces such as a glass wafer is prepared, and an adhesive is coated over one surface of the transparent wafer, where the adhesive is of a negative type. Subsequently, the adhesive coated over the transparent wafer is exposed by a stepper, that is a projection exposure apparatus, via a pattern mask on which shielding patterns each corresponding to one of device formed areas are arranged in, e.g., a matrix of two columns and two rows. Exposure by a stepper is performed multiple times while changing the exposure position so as to cover all corresponding to the device formed areas. Here, the shielding pattern is assumed to be a rectangular pattern corresponding to the shape of the solid-state image sensing device. In exposure, because irradiation light is blocked by the rectangular shielding patterns, portions corresponding to the device formed areas are not exposed.
After exposure, non-exposed portions of the adhesive are removed from the surface of the transparent wafer by a development process. By this means, only exposed adhesive portions 200 (indicated by the hatching) are left on the surface of the transparent wafer 100 as shown in FIG. 1. Adhesive-removed portions 100a are areas corresponding to adhesive portions shielded by the rectangular shielding patterns from the irradiation light and denoted by open rectangles in the figure. Then, a semiconductor wafer having solid-state image sensing devices previously formed in the device formed areas of the surface is stuck to the transparent wafer 100 with the remaining adhesive 200 on the surface of the transparent wafer 100. Hereinafter the semiconductor wafer where the solid-state image sensing device is formed in the device formed areas is called a device formed wafer. Then, the device formed wafer is polished at the back side surface to a desired thickness.
Thereafter, semiconductor devices are finished through the process of forming electrodes and lines on the device formed wafer, the process of cutting the transparent wafer 100 and the device formed wafer into chips, and the process of making modules by fixing a lens to the divided semiconductor chips sealed with glass, and so on.